This invention relates generally to cooling systems for mechanical seals for centrifugal pumps and to cooling systems for magnetic bearings for sealless centrifugal pumps. This invention more particularly relates to the use of a drilled passage in the pump casing to direct cooling flow to selected pump components.
A sealless pump is the type of centrifugal pump that has its impeller and bearing system isolated from the impeller driving mechanism by an isolating wall that seals the pumping mechanism from the surrounding environment and eliminates the necessity to use rotary seals to seal the pumped fluid against leaking along the shaft. U.S. Pat. No. 4,871,301, Centrifugal Pump Bearing Arrangement, illustrates a sealless pump.
Manufacturers of sealless pumps and users of mechanical seals take liquid from behind the impeller via drilled passages in the casing cover or stuffing box to the shell area or mechanical seal chamber. The drilled passage is a hole in the wall of the casing cover or stuffing box. The actual pressure obtained in the drilled passage is much less than the calculated pressure. Tests show that for a particular size pump, the relative pressure of the liquid in the shell area is only 64% of the total head.
The higher the relative pressure in the shell or seal chamber, the more efficient the cooling of the magnetic bearings or the mechanical seals. Tests have also shown that the greater the bolt circle diameter that the drilled passage is located in, the greater the pressure loss in the drilled passage.
The foregoing illustrates limitations know to exist in present cooling systems for mechanical seals or magnetic bearings. Thus, it would be apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.